Long bullets seated deep into short mag brass, effect on accuracy????

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by cdherman, Oct 29, 2011.

  1. cdherman

    cdherman Well-Known Member

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    I have settled on 7mm to rebarrel my Savage short action. Between WSM or SAUM is all that remains in terms of cartrige decisions I think.

    But the real issue is figuring out if I can use the very long Berger 180 VLD hunting bullets. I'd like to not end up with a single shot...

    The new barrel will be throated to a dummy cartridge, so from that standpoint, I can seat the bullet deeper in the case and still get the bullet to sit on the lands, as Berger recomends.

    But what I am concerned with is the effect on case capacity and accuracy that seating those long bullets might have.

    In both the 7mm WSM and 7MM SAUM, to get them to feed in a short action will mean that a chunk of boat-tail and bullet will be down in the case.

    Aside from the obvious loss of case capacity, are there other problems with doing this???

    Accuracy? Brass or barrel life?

    Accuracy is the only one that worries me too much......
     
  2. Mikecr

    Mikecr Well-Known Member

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    You need to figure out the OAL the magazine limits you to & ejection port length & go from there.
    Also, is this a Savage WSM action(they are way different)
    Personally, I don't consider the WSM loaded to potential(with best LR bullets) a short action cartridge.
    There may or may not be a problem seating with bullet bearing past the neck-shoulder junction. It depends on your chamber neck, and dies.
    You would not want to FL size necks for bullets seated so deep.
     

  3. cdherman

    cdherman Well-Known Member

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    The magazine and ejection port issues are easy to figure out. I am mainly concerned with theoretical issues when the bullet is seated deep down in the case.

    You mention not FL sizing -- is that because the neck would have too much bearing surface on the bullet? What would that cause? Too much pressure? Uneven release of the bullet?

    As for the chamber neck and throat -- the throat to the rifling will be custom, based on a dummy cartridge. So I can at least theoretically seat the bullets deep into the case so that I can use the magazine, and then have the throat cut short.

    This would potentially be one of those "designed for one bullet only" guns. But given that it will never see factory ammo, I see no problem with that.

    I am inclined towards the 7mm SAUM -- its actually a tad shorter since apparently the Rem SA is also a tad shorter than the Winchester SA that the WSM was designed for. With the 7mm RSAUM, I would have a little longer neck and a little less case capacity. Probably lose a little velocity, but make up for it in consistency.

    The added downfield speed due to superior BC makes even a slow 7mm look fine, so long as the accuracy is there. Shots over 300 yards pretty much require turret corrections regardless, so what's a 100 fps in the end, so long as its a tack driver shooting a great bullet.....
     
  4. Bart B

    Bart B Well-Known Member

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    There's nothing wrong with full length sizing that case. You may well get best accuracy with it sized that way.

    And seating long, heavy bullets' heels below the neck won't hurt accuracy. .300 Win. Mags. shot in competition have used 200-gr. HPMK bullets so seated and were very accurate; both with new and properly full length sized cases. Uneven release of the bullet is caused by uneven neck tension. Proper full length sizing with a bushing die (no expander ball) will make very uniform neck tension on bullets, especially if the case necks are turned to a uniform thickness and the right size bushing's used.
     
  5. BountyHunter

    BountyHunter Writers Guild

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    Agree with Bart

    Definitely FL size the WSM or SAUM case. They operate way above parameters MikeCR uses for NS only.

    No problems seating longer bullets deeper in the case.

    My original 300 WSM reamer was set up for 190s and I have no problem with 208/210s at the original throat depth. They are back into the case.

    However, IF you are setting it up as a magazine gun, then look into an extended Wyatts mag box and the max COAL for that box. Start your reloading at that point and if needed work back off the max COAL.

    I would lean towards the SAUM vs the 7WSM. The 7WSM is a notorious barrel burner (in as little as 500 rds), especially compared to the SAUM and MV will not be that much different.
     
  6. cdherman

    cdherman Well-Known Member

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    Excellent advice I hope...

    I do not know if the Wyatts box can be used with a Savage SA without the services of a pretty good gunsmith. I'd rather avoid that.

    More over, I got out my calipers and brass last night and started measureing and reading. The SAUM brass is a tad shorter that the WSM. And the Savage SA seems to be generous. If my calculations are correct (which I will verify with a dummy round before I have the barrel made), I can get as much as .92" of exposed bullet into the magazine, and still get it to feed, and eject live rounds when necessary.

    .92 exposed sounds crazy long, but those long Bergers are crazy long too -- the 180 VLD in 7mm is over 1.5" long. That would put about .6"in the case, which would cost me some case capacity and speed.

    As noted, the WSM reputation for burning barrels is not something I like, and with a properly set up scope and rangefinder, its not initial velocity that matters as much as accuracy and down range speed.

    7mm SAUM, here I come......
     
  7. winmagman

    winmagman Well-Known Member

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    cdherman,

    I load the 162 Amax in my Saum to a coal of 2.948 (base to tip) that leaves me .007 off the lands. My cases are trimmed to 2.031, the Amax is 1.414, that leaves me with .917 outside the case. Unfortunately they are about .025 to long to fit in the factory Savage S/A magazine.

    Hope that helps you out some.

    Chris
     
  8. Bart B

    Bart B Well-Known Member

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    I doubt most folks will tell the difference between either the WSM or SAUM versions of 7mm cartridges as to their accurate barrel life. There's only about 5% difference in charge weights in the mid to low 60's for charge weight for a given powder and bullet muzzle velocity. For all practical purposes, both have the same amount of hot burning gasses cutting away at any given point in the throat for the same amount of time.

    Barrel life's round count differs depending on how accurate the barrel was when new to when its owner/shooter notices a loss of accuracy. New barrels that shoot sub 1/4 MOA at 100 yards seem to have half the life as one starting out in the 1/2 to 3/4 MOA level at 100 yards. And then there's conventional service and factory rifles starting out new in the 2 MOA range that go10,000 rounds of seemingly accurate life.

    When one adds in how accurate the owner/shooter shoots them, then a whole new set of numbers show up. Someone shooting squirrels with their Grandpa's .22 rimfire made in the 1930's doesn't mind the fact that a couple hundred thousand rounds have gone down its barrel. But his good friend on the US Olympic Team rebarrels his two year old gold medal winning rifle every 20 to 30 thousand rounds.
     
    Last edited: Oct 30, 2011
  9. Trickymissfit

    Trickymissfit Well-Known Member

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    I'm not going to get into the accuracey thing and seating bullets into the shoulder area, but many people will completely dissagree with you on this point. I have not seen all that much of a problem as long as the base of the bullet is not well into the shoulder area. Still what has to be taken into fact is the reduction of case volume when that bullet moves deep into the shoulder area. So keep that in mind as this mimmics a smaller case. Recommend you start out at the bottom of the ladder and work your way up slowly as the pressures will probably ramp up very quickly. In other words I'd hold to the 10% reduction as a good starting point for your own saftey.
    good luck!
    gary